A study Of Denitrification kinetics At Low Temperatures Using Methanol As The External Carbon Source Open Access
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ABSTRACT The overall objective of this research was to study the denitrification kinetics of methanol utilizing organisms at low temperatures, as methanol is widely used as an external carbon source by the treatment plants in biological denitrification treatment processes to achieve low effluent total nitrogen concentrations. The denitrification parameters studied were the Specific denitrification rates (SDNRs) and the Nitrate half saturation constants (Ks(NO3-N)). Most of the experimental studies were conducted for Blue Plains (BP) Advanced Wastewater Treatment Plant (AWTP), however, few tests were also conducted for samples obtained from the Alexandria Sanitation Authority (ASA) Advanced Wastewater Treatment Plant (AWTP) in Virginia. These tests were conducted at low temperatures in the range of 12°C to 18°C. Respirometer system was used to conduct these tests on mixed liquor taken from the anoxic denitrification zones of the AWTPs using the suspended growth activated sludge process. The respirometer was used to conduct the nitrate-limiting test where nitrate was limited and excess COD and other nutrients were present. A modified specific denitrification rate (SDNR) test was utilized which limited one of the substrates (such as nitrate) to run out before the others. Different KS concentrations may exist not only for the different substrates, but for different processes as well. The maximum specific denitrification rates (SDNR) were found to be in the range of 3.05 to 5.44 mg/gm MLVSS/ hr for temperatures from 12°C to 18°C for samples obtained from BP. A higher temperature resulted in higher SDNRs. The temperature dependency of SDNRs was evaluated and an Arrhenius coefficient (ɵ) of 1.084 was obtained. The average values of nitrate half saturation constant obtained using the nitrate limiting tests (with excess COD present) conducted using respirometery for the same temperature intervals were estimated between 0.02 and 0.99 mg/L. COD to nitrogen ratios in the range of 2.47 to 4.15 were estimated for temperatures from 12°C to 18°C.